Repeater systems are typically used where the area to be covered and/or capacity requirements do not justify the installation of a full Cellular/PCS base station with managed frequency-channel allocation. Thus, as shown in FIG. 1, tower-mounted repeater systems are often used to extend the range of a cell site, to provide null fill in regions that are RF blocked, such as by hills or trees, and/or to provide enhanced xe2x80x9cin-buildingxe2x80x9dcoverage, via directing the signal power to the desired structures, such as a building 30.
The typical repeater system comprises three basic parts shown in FIG. 2 and FIG. 3: the link antenna 22 which is directed/aimed at the wireless base station (BS); the amplifying electronics xe2x80x9cboxxe2x80x9d 24, and the broadcast antenna 26xe2x80x94which is directed towards the area of interest. Often, the link antenna 22 is highly directive (high gain) with a very narrow beam, since it only needs to xe2x80x9cseexe2x80x9d the base station. The broadcast antenna 26 is more defined by the beamwidth necessary to cover the intended area. The electronics box 24 may contain an assortment of diplexers, filters, splitters, and RF amplifiers.
Two of the main performance factors on which a system is based are gain and output power. The output power is mostly determined by the sum of the two passive antenna (link and broadcast) gains and the maximum (linear) output power of the amplifier(s). The system gain is determined by the sum of the passive antenna gains, plus the gain of the amplifier stage. This is limited by the isolation (or mutual coupling) between the two (broadcast and link) antennas. The isolation depends on the antenna type, front to back (F/B) ratio and beamwidth.
For example, assume two opposing antennas, each with 20 dB directivity. Further, assume a F/B ratio of about 25 dB. The isolation between antennas is therefore about 50 dB, which is the sum of the two F/B ratios (25 dB+25 dB). To keep the amplifiers from oscillating, a safety factor of about 20 dB is recommended, which translates to an active (amplifier) gain to about 30 dB (50xe2x88x9220). However, the total system gain is the sum of the passive gains (directivity) plus the active gain, which, in this example, is 20+20+30=70 dB.
Normally, a well designed antenna should have a front to back ratio (F/B) better than 20 dB. For very high gain antennas, the F/B can be as high as 40 dB. However, as the F/B is increased, so typically is the directivity; which means that the antenna""s beamwidth is narrowed. For repeater applications, this might prove disadvantageous, since the coverage area (sector width) is reduced.
Orientation and separation distance of the antennas is also a factor. In the near field, the propagation path loss is proportional to 1/R, where R is the radius or distance between the two antennas (note, it is 1/R2 for the far field). Thus, for two PCS antennas, back to back, seperated by about 10 feet, the propagation loss is about 24 dB. This therefore increases the isolation between the two antennas by 24 dB. However, it is now much harder to accurately orient the antennas, so that they are truly in-line, maximizing their F/B ratio isolation.
This is a significant issue for most operators (customers). Aligning the two antennas, such that they are exactly opposing (one pointed 180 degrees away from the other), can be extremely difficult and time consuming.
Existing indoor repeater systems, typically employ a separate link antenna 32, either on the roof, or on the side of a building (FIG. 4). The RF power is routed to the electronics portion of the repeater via a coaxial cable 34, often with an amplifier stage (not shown) in between. The indoor RF distribution system is either one or more antennas 36, or some other RF emission/reception mechanism, such as radiax (leaky wave) cable, or RF stripline cable 38. The labor for installing these indoor radiation systems (antennas or leaky wave cables) is usually intensive and costly. Additionally, since propagation characteristics inside a building are complex to estimate, or model, multiple radiators are usually used to assure adequate coverage to all portions of the building.
Existing repeater systems, mostly for outdoor use, use physically separate antennas (i.e., physically separate from the amplifier/electronics module/box), one pointed towards the wireless base station, and the other pointed towards the (broadcast) area of interest. This requires mounting/installation of three different units, and labor intensive orientation of the two antennas to maximize the RF isolation, to achieve maximum system gain.
Similar to the outdoor repeater system(s), indoor repeaters require accurate orientation (labor intensive) between the two antennas to insure maximum RF isolation, and to prevent signal feedBack and therefore xe2x80x9cringingxe2x80x9d in the circuit.
A modular repeater comprises a housing having a pair of substantially 180xc2x0 oppositely facing surfaces, at least one antenna element mounted to each of said surfaces for radiating energy in a direction opposite to that of an antenna element mounted to the other of said surfaces, and an electronic circuit mounted within said housing and operatively coupling signals between at least one antenna element on each of said oppositely facing surfaces of said module.